Fluorescent Lamps:
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Screw-in versus Plug-in

Screw-in CFL lamps have a ballast in the base; they can directly screw in into an ordinary light-bulb socket.

Plug-in CFL lamps have either 2-pin or 4-pin bases that plug in to a ballast module. When the lamp reaches end-of-life it is not necessary to throw away the ballast.

Shown below are some examples of plug-in bases and sockets. They have to be properly matched. The main distinction is that there are 2-pin and 4-pin sockets. 2-pin lamps are pre-heat lamps with internal starters, usually magnetic ballasts. 4-pin lamps are electronic ballasts.

Consult the GE catalog for specific information on base and socket names for individual lamps.

Examples of sockets and bases for CFL lamps